1. Field of the Invention
The present invention relates to a throttle grip apparatus which is used to control an engine of a vehicle based on a rotation angle of a throttle grip.
2. Background Art
Recently, there has been popularized a two-wheeled vehicle in which a rotation angle of a throttle grip is detected by a throttle opening angle sensor such as a potentiometer and the detected value is transmitted as an electric signal to an electronic control unit or the like mounted on the two-wheeled vehicle. The electronic control unit executes a given operation according to the electric signal expressing the detected value and, according to an operation result, an ignition time of an engine or an opening/closing of an exhaust valve is controlled.
For example, in JP-A-04-254278, there is disclosed a throttle grip apparatus which has the above-mentioned structure. That is, the throttle grip apparatus mainly includes a drive pulley portion rotatable in linking with a throttle grip, a detecting gear meshingly engageable with a gear formed in a portion of the drive pulley portion, a potentiometer for detecting the rotation angle of the detecting gear, and a case for storing the above composing elements therein. In the throttle grip apparatus, when a driver turns the throttle grip, the potentiometer is rotated through the drive pulley portion, whereby the throttle opening angle of the throttle grip can be detected.
In the above throttle grip apparatus, since the rotation angle of the throttle grip can be detected using the throttle opening angle sensor, there is eliminated a need of an operation cable which has been used in a general-purpose manner in order to transmit the rotation operation of the throttle grip to the engine side. However, in this case, there is removed the sliding resistance that is produced due to the sliding movement of an inner tube with respect to an outer tube constituting the operation cable when the conventional throttle grip is rotated. Thus, a force to be transmitted to the driver in the rotation of the throttle grip provides only the return force of a return spring for returning the throttle grip to its initial position, which gives the driver a strange feeling.
In order to solve such problem, as disclosed, for example, in US2003/0159529, there is proposed an apparatus in which a fixed side friction plate and a rotation side friction plate respectively for applying a friction force in the opposite direction to the rotation direction of the throttle grip when it is rotated are disposed within a case fixed at a position adjacent to the throttle grip, whereby the rotation load of the throttle grip is obtained due to the frictional force of the rotation side friction plate with respect to the fixed side friction plate. According to such conventional throttle grip apparatus, a throttle wire can be omitted and the throttle grip can be operated without applying a strange feeling to the rider.
However, in the above-mentioned throttle grip apparatus, since the resistance force to be produced by the friction plates is constant regardless of the rotation angle of the throttle grip, it is difficult to meet the following requirements of a user: that is, when the rotation angle of the throttle grip is large and it is desired to produce a larger rotation load, or, reversely, when the rotation angle of the throttle grip is small and it is desired to produce a larger rotation load, such larger rotation loads cannot be obtained.